Linseed oil and method for preparation thereof

ABSTRACT

Processed linseed oil essentially consisting of linolenic, linolic and oleic acids, mainly in the form of triglycerides, its content of free tocoferol being less than about 100 ppm; and a process for the manufacture of linseed oil comprising the following steps: a) heating crude linseed oil to an increased temperature lower than the boiling point of water, b) adding a heated inorganic acid to the oil and mixing the oil, c) separation of precipitated materials, d) adding a heated aqueous solution of alkali to the oil and mixing the oil, e) discharge of the soap formed, and f) rinsing the oil with hot water until a clear rinsing water is obtained.

This application is a 371 of PCT/SE00/01862 filed Sep. 26, 2000.

The present invention relates to linseed oil which has been processedfor the purpose of improving the properties of the oil in connectionwith the use in for example impregnation of products based on cellulose,such as wood. The invention also relates to a process for themanufacture of such linseed oil.

Even if the present invention is applicable in relation to othercellulose-based products than wood the invention will in the followingbe described in connection with wood in the form of different types oflumber. Decomposition of wood when used outdoors is almost exclusivelycaused by fungi and bacteria. The requirement for growth of suchmicro-organisms is the presence of water. Furthermore, a suitabletemperature and access to nutrition and oxygen are required. Preventionof decomposition can be based on the elimination of one or more of theseconditions necessary for the growth of the micro-organisms. As anexample there can be mentioned that if the moisture content is broughtdown to a value lower than about 20% biological decomposition issubstantially prevented.

A number of different impregnation processes for the protection of woodare known, and these methods can in principle be divided up intotechniques based on the supply of a substance poisonous to the growth ofthe micro-organisms, and techniques whereby the wood is given hydrofobicproperties, for example by impregnation with some kind or oil. In thelatter case an impregnation agent is crude linseed which can be of hot-or cold-pressed type, both of which by suitable heat treatment areconcerted into boiled linseed oils. The use of such linseed oils is,however, associated with certain drawbacks for example a viscosity whichis unfavourably high for ease of handling, a contents of componentsconstituting substrate for the relevant micro-organisms, unfavourabledrying properties, etc. One method used for lowering the viscosity isdilution with a solvent something which, however, is environmentallyunacceptable. The use of chemical poisons is presently frequently usedbut should for the future be mainly prohibited for environmentalreasons. Also impregnation with a combination of hydrofobation and toxictreatment is used, for example treatment with creosote.

The present invention has for an object to provide a processed linseedoil with properties which are substantially improved, mainly inconnection with the use of the linseed oil for the impregnation of woodand wood products.

Another object of the invention is to provide a process for themanufacture of such linseed oil of improved properties.

Yet an object of the invention is to provide a process, whereby theuptake of the oil by the wood or the wood product in connection withimpregnation is substantially increased and can even reach a near 100percent level of uptake.

In connection with extensive research and experimental work it has inaccordance with the invention been found that a treatment of linseed oilresulting a situation that its content of free tocoferol will be lessthan about 100 ppm, results in substantially improved properties of thelinseed oil, particularly in connection with its use as an impregnatingagent for wood or lumber.

These and other objects of the invention which will be clear from thefollowing description are obtained by a processed linseed oilessentially consisting of linolenic, linolic and oleic acids, mainly inthe form of triglycerides, the linseed oil being characterized in thatits contents of free tocoferol is less than about 100 ppm.

It is particularly preferred that the processed linseed oil containsfree tocoferol in a concentration less than about 75 ppm andparticularly less than about 50 ppm.

Even if the processed linseed oil according to the present invention canbe based on cold pressed as well as hot pressed linseed oil it ispreferred to use cold-pressed linseed oil as a starting material for thelinseed oil according to the invention.

The new process according to the invention for the manufacture of alinseed oil of the above type is characterized by the following steps:

a) heating crude linseed oil to an increased temperature lower than theboiling point of water,

b) adding a heated inorganic acid to the oil and mixing the oil,

c) separation of precipitated materials, for example by sedimentationand discharge and removal of bottom deposit formed,

d) adding a heated aqueous solution of alkali to the oil and mixing theoil,

e) discharge of the soap formed, and

f) rinsing the oil with hot water until a clear rinsing water isobtained.

The heating in step a) above suitably takes place at a temperature lyingwithin the range about 80 to about 99° C. while avoiding that theboiling point of water will be reached.

The inorganic acid is preferably added in an amount of about 0.5 to 30%by weight based on the weight of the oil. Among suitable inorganic acidsthere may be mentioned phosphoric acid, sulphuric acid and hydrochloricacid. It is preferred to use as an inorganic acid phosphoric acid, forexample thermal phosphoric acid, at a concentration of for example 80%and in a quantity of about 0.5 to about 2% by weight, particulary fromabout 1 to about 1.5% by weight.

The mixing in step b) suitably lasts until the reaction has come to astop, which corresponds to a period of about 10 to about 30 minutes.

As alkali any suitable alkaline compound can be used, for examplehydroxides of alkali or earth alkali metals, particularly sodiumhydroxide or potassium hydroxide. Particularly preferred is sodiumhydroxide, also called caustic soda. The alkaline compound is suitablyadded in a quantity equivalent to about 2 to 5% by dry weight based onthe weight of the oil. Alkali is suitably added in the form of anaqueous solution in a quantity of about 7 to 15% by weight water alsothis based on the weight of the oil.

For the purpose of avoiding thickening of the oil during heating the oilmay in a further step be heated while adding a suitable agent, such asmanganese tetraborate. A suitable temperature range for the heating ofthe oil in this further step is from about 120 to about 140° C. In orderto improve the trying properties of the processed oil a suitablecatalyst can be added, for example example manganese tetraborate. Theagent used as a catalyst can be the same as the agent used to avoidthickening of the oil during heating.

The invention will in the following be further described with referenceto non-limiting examples, wherein quantities and percentages relate toweight if not otherwise stated. In the examples abbreviations concerningthe fatty acid present in the linseed oil are furthermore used.Accordingly, for example oleic acid is abbreviated C18:1, linolic acidC18:2 and linolenic acid C18:3. The number following the colon thusindicates the degree of unsaturation.

EXAMPLE 1 Manufacture of Processed Linseed Oil

As a starting material in the treatment of the oil Swedish cold-pressedcrude linseed oil is used. The treatment of this linseed oil takes placeas follows.

The crude cold-pressed linseed oil is heated to about 90° C., and 1.2%hot 80% thermal phosphoric acid is then added to the linseed oil andmixing is carried out for about 20 minutes. The bottom deposit in theform of a black precipitate formed during this acid treatment is removedby sedimentation and discharge.

Then 3.7% 100% caustic soda dissolved in 11% heated water is added tothe acid-treated linseed oil, and mixing then takes place for 7-10minutes while observing the course of reaction. The soap formed in thisalkali treatment is discharged and the linseed oil obtained is purifiedby rinsing with 25% by volume heated water 5 to 7 times or until therinsing water is clear and has a pH-value normal to water.

By this treatment substantially all of the no-desired components of thelinseed oil have been removed, particularly its original contents oftocoferol. In order that the oil shall possess drying properties it isthen heated to about 127° C. for about 6 hours, about 0.02% manganesetetraborate being used as a catalyst, the reason being that the oilshall not thicken during boiling.

In the following examples analysis of processed linseed oils accordingto the present invention prepared as described above are given and alsocorresponding analysis data for conventional products available on themarket.

EXAMPLE 2 Analysis of Processed Linseed Oil According to the Inventionand Two Commercially Available Linseed Oils

In the table below the designations for the linseed oils are KH.KF Eg1382 boiled linseed oil varnish made from Swedich cold-pressed crudelinseed oil from the harvest of 1998. The two commercially availableoils FK.K Eg 1382 and AC.K Eg 1383 are linseed oils sold byFärghandelskompaniet in Malmö, hot-pressed boiled linseed oil and Alfort& Cronholm Grosshandel AB, Stockholm, also hot-pressed boiled linseedoil, respectively.

TABLE I Fatty acid composi- FK.K Eg KH.KF Eg ACK Eg IUPAC 2.302 tion, %1381 1382 1383 (m) C16:0 5,1 4,1 5,1 C18:0 3,6 3,3 3,6 C18:1 18,1  12,2 18,1  C18:2 15,6  14,8  15,7  C18:3 55,9  64,1  55,9  C20:0 0,2 0,1 0,1C20:1 0,2 0,2 0,2 C22:0 0,1 0,1 0,1 C24:0 0,1 0,1 0,1 C24:1 0,3 0,4 0,2Unknown 0,8 0,7 0,9 Tocoferol, ppm IUPAC 2.432 Alpha <5 <5 <5 Alpha T3<5 <5 <5 Gamma 170 <5 168 Gamma T3 <5 <5 <5 Delta 5 <5 5 Delta T3 <5 <5<5 Phosphorus AAS, 250 40 250 IUPAC 2.423 mg/kg (m)

As is clear from the analysis data given above the content of freetocoferol has been largely lowered to 0 in the linseed oil according tothe invention. Furthermore, a substantial decrease of oleic acid and aneven greater decrease of the amount of phosphorus present can be noted.

EXAMPLE 3 Analysis of Processed Linseed Oil According to the Inventionand Three Commercially Available Linseed Oils

In the table below the designations for the linseed oils are KH.KI Eg1387 boiled impregnating linseed oil from the harvest of 1998. The threecommercially available oils BE.K. Eg 1384 is boiled linseed oil fromBeckers, Stockholm, AL.R. Eg 1385 is Swedish cold-pressed crude linseedoil from Alcro Färg, Stockholm and E{dot over (A)}.R. Eg 1386 ishot-pressed crude linseed oil from Eskil {dot over (A)}kerberg AB,Malmö, respectively.

TABLE II BE.K AL.R EA.R KH.KI Eg Eg Eg Eg 1384 1385 1386 1387 Fatty acidIUPAC 2.302 (m) composition % C16:0 5,0 5,2 5,0 4,3 C18:0 3,6 3,8 3,13,8 C18:1 18,0  13,5  20,8  14,8  C18:2 15,5  18,0  15,0  14,5  C18:356,5  58,0  54,0  61,1  C20:0 0,1 0,1 0,2 0,1 C20:1 0,2 0,1 0,3 0,2C22:0 0,1 0,1 0,2 0,1 C22:1 <0,1   <0,1   0,1 <0,1   C24:0 0,1 0,1 0,10,1 C24:1 0,3 0,4 0,3 0,3 Unknown 0,6 0,7 0,9 0,7 Tocoferol, ppm IUPAC2.432 Alpha <5 <5 <5 <5 Alpha T3 <5 <5 <5 <5 Gamma 105 350 230 <5 GammaT3 <5 <5 <5 <5 Delta 5 5 5 <5 Delta T3 <5 <5 <5 <5 Phosphorus 206 20 8725 IUPAC 2.423 (m) AAS, mg/kg

Also in this analysis report it can be noted that the processed linseedoil according to the invention is largely free from tocoferol, whereasthe contents of oleic acid and phosphorus are lower than in two of thecommercial oils, whereas the third commercial oil also has relativelylow contents of oleic acid and phosphorus.

Tests carried out with the processed linseed oil according to thepresent invention show that it has substantially improved properties,particularly in connection with its use for the impregnation of wood andwood products. Thus, the oil according to the invention has lowerviscosity and thereby improved handling, it has also by the treatment alower contents of substances constituting substrates formicro-organisms, and it gives when used for impregnation of woodsubstantially improved resistance.

Thus, accelerated tests in fungus cellar have shown that the linseed oilaccording to the invention has substantially improved rot-resistancecompared with CCA-impregnated wood products (CCA=chromium, copper,arsenic). The same holds for rot-resistance for impregnated rodsinserted into moist earth in cellar climate of high relative moistureand temperature. Moreover, rot-resistance tests have been carried outwith impregnated rods inserted into the ground on fields withmicro-organism flora and aggressive brown rot shown that impregnationwith the processed linseed oil according to the invention results insubstantially improved rot-resistance compared with bothCCA-impregnation and impregnation with conventional linseed oils.

It should be observed that the present invention is not restricted tothe specific embodiments exemplified above. Thus, modifications andchanges can be carried out within the frame-work of the invention andsuch changes and modifications are easily understood by those skilled inthe art.

What is claimed is:
 1. Processed linseed oil essentially consisting oflinolenic, linolic and oleic acids, mainly in the form of triglycerides,characterized in that its content of free tocoferol is less than about75 ppm.
 2. Linseed oil according to claim 1, characterized in that itscontent of free tocoferol is less than about 50 ppm.
 3. Linseed oilaccording to claim 1, characterized in that it is based on cold-pressedlinseed oil.
 4. A process for the manufacture of a linseed oil accordingto claim 1, characterized by the following steps: a) heating crudelinseed oil to an increased temperature lower than the boiling point ofwater, b) adding a heated inorganic acid to the oil and mixing the oil,c) separation of precipitated materials, d) adding a heated aqueoussolution of alkali to the oil and mixing the oil, e) discharge of thesoap formed, and f) rinsing the oil with hot water until a clear rinsingwater is obtained.
 5. A process according to claim 4, characterized inthat the heating in step a) takes place to a temperature less than about80° C.
 6. A process according to claim 4, characterized in that theinorganic acid is added in a quantity of about 0.5 to 30% by weightbased on the weight of the oil.
 7. A process according to claim 4,characterized in that the mixing in step b) is carried out for a periodof time of about 10 to 30 min.
 8. A process according to claim 4,characterized in that there is used as an alkali caustic soda insolution, suitably added in a quantity equivalent to about 2 to 5% byweight dry weight based on the weight of the oil.
 9. A process accordingto claim 8, characterized in that caustic soda is added dissolved inabout 7 to 15% by weight of heated water based on the weight of the oil.10. A process according to claim 6, characterized by a further stepafter the rinsing step f) constituted by heating the oil while adding anagent preventing thickening of the oil during heating.
 11. A processaccording to claim 10, characterized in that the oil is heated to atemperature of about 120 to 140° C.
 12. A process according to claim 10,characterized in that manganese tetra borate is used as said agentsimultaneously acting as a catalyst.
 13. Linseed oil according to claim2, characterized in that it is based on cold-pressed linseed oil.
 14. Aprocess for the manufacture of a linseed oil according to claim 2,characterized by the following steps: a) heating crude linseed oil to anincreased temperature lower than the boiling point of water, b) adding aheated inorganic acid to the oil and mixing the oil, c) separation ofprecipitated materials, d) adding a heated aqueous solution of alkali tothe oil and mixing the oil, e) discharge of the soap formed, and f)rinsing the oil with hot water until a clear rinsing water is obtained.15. A process for the manufacture of a linseed oil according to claim 3,characterized by the following steps: a) heating crude linseed oil to anincreased temperature lower than the boiling point of water, b) adding aheated inorganic acid to the oil and mixing the oil, c) separation ofprecipitated materials, d) adding a heated aqueous solution of alkali tothe oil and mixing the oil, e) discharge of the soap formed, and f)rinsing the oil with hot water until a clear rinsing water is obtained.16. A process according to claim 5, characterized in that the inorganicacid is added in a quantity of about 0.5 to 30% by weight based on theweight of the oil.
 17. A process according to claim 5, characterized inthat the mixing in step b) is carried out for a period of time of about10 to 30 min.
 18. A process according to claim 6, characterized in thatthe mixing in step b) is carried out for a period of time of about 10 to30 min.
 19. A process according to claim 4, characterized in that thereis used as an alkali caustic soda in solution, suitably added in aquantity equivalent to about 2 to 5% by weight dry weight based on theweight of the oil.
 20. A process according to claim 5, characterized inthat there is used as an alkali caustic soda in solution, suitably addedin a quantity equivalent to about 2 to 5% by weight dry weight based onthe weight of the oil.
 21. A process according to claim 6, characterizedin that there is used as an alkali caustic soda in solution, suitablyadded in a quantity equivalent to about 2 to 5% by weight dry weightbased on the weight of the oil.
 22. A process according to claim 7,characterized in that there is used as an alkali caustic soda insolution, suitably added in a quantity equivalent to about 2 to 5% byweight dry weight based on the weight of the oil.
 23. A processaccording to claim 7, characterized by a further step after the rinsingstep f) constituted by heating the oil while adding an agent preventingthickening of the oil during heating.
 24. A process according to claim8, characterized by a further step after the rinsing step f) constitutedby heating the oil while adding an agent preventing thickening of theoil during heating.
 25. A process according to claim 9, characterized bya further step after the rinsing step f) constituted by heating the oilwhile adding an agent preventing thickening of the oil during heating.26. A process according to claim 11, characterized in that manganesetetra borate is used as said agent simultaneously acting as a catalyst.